Poly[di(2-cyanoethyl)phosphonylmethyl]aromatic compounds are known flame-retardant compounds for thermoplastic polymers. They are described by Hoffman in U.S. Pat. Nos. 3,835,119, 3,895,048, and 3,917,560. The preparation of the compounds is described in U.S. Pat. No. 3,895,048, whereby various (2-cyanoethyl)phosphine oxides are reacted with an appropriately substituted halomethyl aromatic compounds, for example, 1,4-bis-(chloromethyl) benzene.
Although that method is very effective for the preparation of poly[di(2-cyanoethyl)phosphonylmethyl]aromatic compounds, problems are frequently encountered when attempts are made to utilize the method for the preparation of their mono- or poly[dialkylphosphonylmethyl]aromatic analogs. Thus, in many instances the appropriate phosphine oxide either is unavailable or the reaction to prepare the phosphine oxide does not proceed as expected. For instance, attempts to prepare bis (cyclohexyl)phosphine oxide by oxidation of the corresponding phosphine lead to the formation of the phosphinic acid.
There is a need, therefore, for a generally applicable method for the preparation of mono- or poly[dialkyl- or dicycloalkylphosphonylmethyl]aromatic carbocyclic compounds.